U.S. patent number 5,417,731 [Application Number 08/120,501] was granted by the patent office on 1995-05-23 for method of heating a charge, including injecting secondary oxidant into the output port.
This patent grant is currently assigned to Owens-Brockway Glass Container, Inc., Praxair Technology, Inc.. Invention is credited to Thomas K. Dankert, John R. LeBlanc, Geoffrey B. Tuson.
United States Patent |
5,417,731 |
LeBlanc , et al. |
May 23, 1995 |
**Please see images for:
( Certificate of Correction ) ** |
Method of heating a charge, including injecting secondary oxidant
into the output port
Abstract
A combustion method wherein oxidant and fuel are provided into a
charged furnace in a substantially stoichiometric ratio for
relatively complete combustion and secondary oxidant is provided in
a defined manner outside the furnace for further combustion without
excessive NO.sub.x or carbon monoxide formation.
Inventors: |
LeBlanc; John R. (Perrysburg,
OH), Dankert; Thomas K. (Sylvania, OH), Tuson; Geoffrey
B. (Yorktown Heights, NY) |
Assignee: |
Owens-Brockway Glass Container,
Inc. (Danbury, CT)
Praxair Technology, Inc. (Danbury, CT)
|
Family
ID: |
22390708 |
Appl.
No.: |
08/120,501 |
Filed: |
September 14, 1993 |
Current U.S.
Class: |
65/134.4;
65/134.6; 432/161 |
Current CPC
Class: |
C03B
5/2353 (20130101); C03B 5/235 (20130101); Y02P
40/50 (20151101); Y02P 40/55 (20151101) |
Current International
Class: |
C03B
5/00 (20060101); C03B 5/235 (20060101); C03B
005/04 () |
Field of
Search: |
;431/10,174,178
;432/161,30,180,54 ;65/135,134.6,134.4,27 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Sieger, W. et al., Korting Hanover AG, Reducing NO.sub.x Emission
At Glass Melting Furnaces, pp. 99-101..
|
Primary Examiner: Jones; W. Gary
Assistant Examiner: Hoffmann; John
Attorney, Agent or Firm: Ktorides; Stanley
Claims
We claim:
1. A method for carrying out combustion comprising:
(A) providing fuel and oxidant in a substantially stoichiometric
ratio into a furnace which contains a charge and which communicates
with a flue system through an exhaust port of the flue system, said
exhaust port having a smaller cross-sectional area than the
cross-sectional area of the furnace;
(B) combusting said fuel and oxidant within the furnace to produce
combustion reaction gases including carbon monoxide, and to
generate heat for heating the charge;
(C) passing the combustion reaction gases from the furnace into and
through the exhaust port of the flue system;
(D) injecting secondary oxidant into the exhaust port at a velocity
of at least 20 feet per second at a location where the temperature
of the combustion reaction gases is at least 1600.degree. F;
and
(E) reacting the secondary oxidant with the carbon monoxide
contained in the combustion reaction gases within the exhaust port
of the flue system to produce carbon dioxide.
2. The method of claim 1 wherein the charge comprises glass or
glassmaking materials.
3. The method of claim 1 wherein the secondary oxidant is injected
into the exhaust port of the flue system in a direction toward the
furnace counter to the flow direction of the combustion reaction
gases passing through the exhaust port of the flue system.
4. The method of claim 1 wherein the secondary oxidant has an
oxygen concentration of at least 80 mole percent.
5. The method of claim 1 wherein the temperature of the combustion
reaction gases at the secondary oxidant injection location is at
least 2000.degree. F.
Description
TECHNICAL FIELD
The invention relates generally to furnace combustion wherein heat
is produced to heat a charge.
BACKGROUND ART
Many industrial processes employ furnaces wherein fuel and oxidant
are combusted to generate heat which is used to heat a charge
within the furnace. Among such industrial processes one can name
glassmaking wherein the charge is glassmaking materials or molten
or solid glass, steelmaking wherein the charge is steel or iron and
aluminum melting wherein the charge is aluminum ingots or
scrap.
In carrying out such furnace combustion it is desirable to
completely combust the fuel within the furnace as this serves to
maximize the amount of heat released within the furnace and
available to heat the charge. Accordingly, oxidant and fuel may be
provided into the furnace in a ratio which is not substoichiometric
since a substoichiometric ratio would cause some of the fuel to
remain unburned or would result in the generation of significant
amounts of products of incomplete combustion such as carbon
monoxide, hydrocarbons and carbon.
At first glance it would appear that the optimum ratio for
providing oxidant and fuel into a furnace for combustion is one
that is substantially stoichiometric. However, in practice, such
firing leads to some incomplete combustion because of less than
perfect mixing of fuel and oxidant within the furnace and also
because the reaction kinetics of the fuel and oxidant may not
enable all of the fuel to completely combust prior to exiting the
furnace. Accordingly, in actual industrial practice, furnaces of
this type are operated with excess oxygen to ensure the complete
combustion of the fuel within the furnace. Unfortunately, when
furnaces are operated in this way, i.e., where oxidant and fuel are
provided into the furnace in a superstoichiometric ratio, there
arises the tendency to generate excessive levels of nitrogen oxides
(NO.sub.x) because oxygen in excess of that needed to react with
the fuel becomes available to combine with nitrogen to form
NO.sub.x. NO.sub.x is a significant pollutant and there exists a
need to reduce the amount of NO.sub.x generated when carrying out
combustion.
Accordingly, it is an object of this invention to provide a method
for carrying out essentially complete combustion to generate heat
efficiently within a furnace to heat a charge while avoiding the
generation of high Levels of NO.sub.x.
SUMMARY OF THE INVENTION
The above and other objects which will become apparent to one
skilled in the art upon a reading of this disclosure are attained
by the present invention which is:
A method for carrying out combustion comprising:
(A) providing fuel and oxidant in a substantially stoichiometric
ratio into a furnace which is in flow communication with a flue
system and which contains a charge;
(B) combusting said fuel and oxidant within the furnace to produce
combustion reaction gases including carbon monoxide, and to
generate heat for heating the charge;
(C) passing combustion reaction Bases from the furnace into the
flue system;
(D) injecting secondary oxidant at a velocity of at least 20 feet
per second into the flue system at a location where the temperature
of the combustion reaction gases is at least 1600.degree. F.;
and
(E) reacting secondary oxidant with carbon monoxide contained in
the combustion reaction gases within the flue system to produce
carbon dioxide.
As used herein, the term "substantially stoichiometric" means not
less than 99 percent or more than 105 percent of
stoichiometric.
As used herein, the term "flue system" means a passage
communicating with a furnace by a conduit having a narrower
cross-sectional flow area than does the furnace, said passage
capable of passing furnace gases from the furnace to the ambient
atmosphere.
As used herein the term "ambient atmosphere" means the outside
atmosphere or an inside atmosphere which can pass or leak into the
outside atmosphere.
As used herein, the term "charge" means material within a furnace
which is intended to be heated and in some cases melted.
BRIEF DESCRIPTION OF THE DRAWING
The sole FIGURE is a simplified plan view representation of one
embodiment of the invention as it may be practiced in conjunction
with a cross-fired furnace.
DETAILED DESCRIPTION
The invention will be described in detail with reference to the
drawing.
Referring now to the FIGURE there is illustrated a plan view of
cross-fired glassmelting furnace 10. The practice of this invention
will have particular utility in regenerative glassmelting furnaces
where physical obstructions make introducing secondary oxidant into
the combustion chamber difficult. Other types of furnaces wherein
the invention may be advantageously practiced include steel
reheating furnaces and aluminum melting furnaces. Furnace 10
contains a charge 2 of glassmaking materials and molten glass which
pass through the furnace underneath the cross-fired flames.
Fuel and furnace oxidant are provided into the furnace in a
substantially stoichiometric ratio through one or more burners or
ports 11. In the embodiment illustrated in the FIGURE, five such
burners are shown. The fuel may be any fluid fuel such as methane,
propane, natural gas or fuel oil. The oxidant may be air or a fluid
having an oxygen concentration greater than that of air.
Within furnace 10 the fuel and oxidant combust such as is
illustrated by flames 1 in the FIGURE. The combustion generates
heat which is employed within the furnace to heat, and in some
cases to melt, the charge. In carrying out the combustion there are
produced combustion reaction gases. The temperature of the
combustion reaction gases produced in the furnace is generally
within the range of from 2200.degree. to 3100.degree. F. Because of
the substantially stoichiometric ratio at which the fuel and
oxidant are provided into the furnace, most of the combustion
reaction gases produced are products of complete combustion, i.e.,
carbon dioxide and water vapor. However, there are also produced
some products of incomplete combustion including carbon monoxide
and perhaps hydrocarbons and carbon in the combustion reaction
gases.
The combustion reaction gases are passed from the furnace into the
flue system. In the embodiment illustrated in the FIGURE the flue
system comprises chimney system 5, which can pass the gases into
the ambient atmosphere, and exhaust port 3 which communicates with
the furnace. The cross-sectional flow area 12 where the flue system
communicates with the furnace is smaller than the cross-sectional
flow area of the furnace through which the combusting fuel and
oxidant travel. The embodiment illustrated in the FIGURE
illustrates five exhaust ports each corresponding to a burner. It
will be recognized by one skilled in the art that the invention may
be practiced with any practical number of burners and exhaust ports
including one burner and/or one exhaust port.
Secondary oxidant is injected into the flue system, preferably, as
illustrated in the FIGURE, into the exhaust port or ports. The
secondary oxidant is injected into the flue system through lance 4.
As mentioned, the FIGURE is a simplified representation intended to
illustrate the method of this invention. Accordingly, there is not
shown the sources of fuel and oxidant. Those skilled in the art
will readily recognize the fuel and oxidant are provided to the
burners and lances from appropriate sources through conduits which
are not shown. The secondary oxidant may be air or a fluid having
an oxygen concentration greater than that of air. Preferably the
secondary oxidant has an oxygen concentration of at least 80 mole
percent and most preferably greater than 90 mole percent.
A high oxygen concentration in the secondary oxidant is preferred
because this enables a smaller volume of secondary oxidant to
oxidize a given quantity of products of incomplete combustion.
Therefore the pressure of the secondary oxidant and/or the size of
conduits and lances for secondary oxidant can be reduced. The
volume of gas to be passed through the flue system is also reduced,
which can be advantageous if the flue system area is restricted due
to factors such as clogging by particulates, as often happens in
glassmelting facilities. High secondary oxidant oxygen
concentration is also preferable if a system is in place to capture
useful heat from the furnace exhaust gases, as in the case of
regenerative glass melting furnaces. Since less diluent, which is
mostly nitrogen, is present in the secondary oxidant, furnace fuel
efficiency is impacted less by heat being absorbed and carried away
by the diluent gases.
The concentration of products of incomplete combustion within the
combustion reaction gases passing through the flue system is
relatively low because the oxidant and fuel are provided into the
furnace in a substantially stoichiometric ratio and not at a
significantly substoichiometric ratio. In order for the secondary
oxidant to effectively burn out the products of incomplete
combustion, some residence time at a high temperature is required.
This is achieved by injecting the secondary oxidant into the flue
system at a location where the combustion reaction gases are at a
temperature of at least 1600.degree. F. Below 1600.degree. F. the
reaction kinetics of the oxidation of carbon monoxide proceed too
slowly for the effective utilization of the method of this
invention. Preferably the temperature of the combustion reaction
gases at the secondary oxidant injection location will be at least
2000.degree. F.
The secondary oxidant injection must create sufficient turbulence
or flow disruption to mix with and combust the relatively dilute
products of incomplete combustion which may include hydrocarbons in
addition to carbon monoxide. Such desired flow effects are attained
by injecting the secondary oxidant into the flue system at a
velocity of at least 20 feet per second and preferably within the
range of from 50 to 300 feet per second. In addition, as
illustrated in the FIGURE it is preferred that the secondary
oxidant is injected into the flue system in a direction toward the
furnace, i.e., in a direction counter to the flow direction of the
combustion reaction gases passing through the flue system.
Within the flue system the secondary oxidant reacts with carbon
monoxide in the combustion reaction gases to produce carbon
dioxide. If hydrocarbons are also present within the combustion
reaction gases, the secondary oxidant will react with such
hydrocarbons to produce carbon dioxide and water vapor. The
injection of secondary oxidant into the exhaust port of the flue
system is particularly preferred because the combustion reaction
gases are at their highest temperature at this location. As
discussed previously, high temperature promotes rapid reaction
between the combustion reaction gases and the secondary oxidant.
Furthermore, the confined volume of the exhaust port contributes to
the ability of the secondary oxidant to react with the dilute
carbon monoxide and maximizes the burnout of the products of
incomplete combustion.
The method of this invention is advantageous over conventional
combustion methods which seek to reduce the level of products of
incomplete combustion which reach the ambiant atmosphere from a
furnace by providing oxidant and fuel into the furnace in an
oxygen-rich or excess air mode because such oxygen-rich operation
is vulnerable to excessive NO.sub.x generation. Moreover,
conventional combustion staging systems which supply secondary
oxygen directly into the furnace have the disadvantage, in the case
of some furnace geometries, of the difficulty of providing the
additional oxygen in a manner which enables effective combustion of
a significant amount of the products of incomplete combustion
within the furnace.
Although the invention has been described in detail with reference
to a certain preferred embodiment, those skilled in the art will
recognize that there are other embodiments of the invention within
the spirit and scope of the claims.
* * * * *